class EventDispatcher {

    addEventListener(type, listener) {

        if (this._listeners === undefined) this._listeners = {};

        const listeners = this._listeners;

        if (listeners[type] === undefined) {

            listeners[type] = [];

        }

        if (listeners[type].indexOf(listener) === - 1) {

            listeners[type].push(listener);

        }

    }

    hasEventListener(type, listener) {

        if (this._listeners === undefined) return false;

        const listeners = this._listeners;

        return listeners[type] !== undefined && listeners[type].indexOf(listener) !== - 1;

    }

    removeEventListener(type, listener) {

        if (this._listeners === undefined) return;

        const listeners = this._listeners;
        const listenerArray = listeners[type];

        if (listenerArray !== undefined) {

            const index = listenerArray.indexOf(listener);

            if (index !== - 1) {

                listenerArray.splice(index, 1);

            }

        }

    }

    dispatchEvent(event) {

        if (this._listeners === undefined) return;

        const listeners = this._listeners;
        const listenerArray = listeners[event.type];

        if (listenerArray !== undefined) {

            event.target = this;

            // Make a copy, in case listeners are removed while iterating.
            const array = listenerArray.slice(0);

            for (let i = 0, l = array.length; i < l; i++) {

                array[i].call(this, event);

            }

            event.target = null;

        }

    }

}


export { EventDispatcher };
